As discussed below, the purpose of this invention is, in general, to deliver a beam having a very small waist at normal incidence into a target. Although it is to be understood that the invention is not limited to such an application the invention is particularly adapted to provide proper launching of a laser beam into a target in the form of the core of a polarization-preserving optical fiber. Seven adjustments ar generally necessary to achieve this, and, in particular, these seven adjustments comprise adjustment of: (i) the beam polarization; (ii) the diameter of the beam waist at the target (the optical fiber core); (iii) the relative axial (z) position of the beam waist with respect to the optical target; (iv) the relative transverse (x) position of the beam waist with respect to the optical fiber; (v) the relative transverse (y) position of the beam waist with respect to the optical target; (vi) the input angle in the horizontal plane; and (vii) the input angle in the vertical plane.
Turning to a consideration of the prior art, one approach for launching a laser beam into an optical fiber involves the use of a single lens having a focal length chosen to provide a beam having an output waist of the proper diameter to match the input waist requirement of the fiber. However, such an approach, i.e., one using a single lens, provides none of the seven required adjustments discussed above. Therefore, all adjustments, and the attendant requirements for resolution and stability, are entirely the burden of the associated mechanical system.
Considering other prior art in this field, Catalog No. 100 of The Newport Corporation, at page J-16, describes fiber couplers F-1015 and F-1015LD that are said to solve some of the difficulties with other prior art systems, by providing certain adjustments which are made optically. Both of the couplers referred to above use two optical elements, viz., a negative lens and a positive lens, to provide very accurate transverse positioning adjustments in the x and y directions, i.e., adjustments corresponding to adjustments (iv) and (v) above.
Considering other prior art systems it is noted that in those instances where the target can be mounted on a mechanical positioner, linear and angular adjustments can be accomplished with the required accuracy using piezoelectric manipulators. However, the expense of this approach is generally prohibitive.
In summary, prior art systems employing optical techniques to launch a laser beam into optical fiber or other target simply do not provide the necessary adjustments discussed above. In this regard, as stated, the Newport couplers provide only two of the required adjustments, while the single lens arrangement provides none.
There are, of course, many patents relating to positioning and/or focussing of laser energy and one patent of possible interest is U.S. Pat. No. 4,556,284 (Albersdoerfer et al) which discloses an apparatus for combining an optical and laser system and including a self-focussing optical fiber bundle the emitting surface of which is mounted so as to introduce the laser energy into the optical system at a favorable location.